I don't think most communists would have a problem with people trading crops that they grow themselves. The problem comes in when someone hires employees to grow more crops for them, starts collecting profits, and grows the farm even bigger. All under the expectation that they own everything that their employees worked for. Cause that's literally capitalism on a small scale.

Of course it needs to be possible for multiple people to come together and start growing crops, but only as long as no single person can take over the entire operation. Leaders would be elected, and be given a somewhat higher salary to reflect the additional responsibility.